Initial radiometric calibration status and performance of NOAA-20 VIIRS reflective solar bands

Abstract

The Earth-observing Visible Infrared Imaging Radiometer Suite (VIIRS) on the NOAA-20 satellite (formerly the Joint Polar Satellite System-1) is the follow-on sensor to the early launched VIIRS on the Suomi National Polar-orbiting Partnership (SNPP) satellite. The on-orbit radiometric calibration of its reflective solar bands (RSBs) is regularly performed primarily through observations of an onboard sunlit solar diffuser (SD). The on-orbit change of the SD bidirectional reflectance distribution function (BRDF) value, denoted as the H-factor, is determined by an onboard solar diffuser stability monitor (SDSM). The scene spectral radiance is calculated by a quadratic polynomial of the background subtracted detector digital number for most of the RSBs and a cubic polynomial for the M8-11 bands. A numerical factor, denoted as the F-factor, provides an on-orbit adjustment to the prelaunch polynomial coefficients through observations of the sunlit SD. The accuracy and change in the F-factor directly affect the sensor radiometric performance. The accuracy of the F-factor is proportionally affected by the accuracy in the H-factor. In this paper, we show the time trends of the Hand F-factors and the SDSM detector gain, and also compare the trends with those for the previous VIIRS instrument on the Suomi National Polar-orbiting Partnership satellite. We derive the Earth view signal-to-noise ratio at the typical spectral radiance level and estimate the calibration bias between the two VIIRS instruments through observations of the Moon and pseudo-invariant Earth sites.